Liquid phase epitaxial growth is a common step carried out during the fabrication of many different types of solid state devices. As used herein, "liquid phase epitaxial growth" includes both growth and regrowth. The prior art has recognized that defects in a solid state device can arise when liquid phase epitaxial growth is used for fabricating a solid state device having chemically bound phosphorus.
Generally, liquid phase epitaxial growth is carried out by initially heating a wafer or substrate, thereafter, allowing epitaxial growth, and subsequently, cooling the wafer or substrate. Loss of P and/or As atoms can occur during the initial heating and cooling steps.
The article entitled, "Prevention of InP Surface Decomposition in Liquid Phase Epitaxial Growth" by G. A. Antypas, Appl. Phys. Lett. 37 (1), July 1980, pp. 64-65, discloses that loss of P atoms during liquid phase epitaxial growth can produce defects. The article discloses that the loss of P atoms can be inhibited by carrying out the initial heating step prior to the liquid phase epitaxial growth in the presence of a partial pressure of phosphorus which is greater than the decomposition pressure of phosphorus of InP. The partial pressure of phosphorus was obtained using InP dissolved in tin, i.e. an InP-Sn solution. The article discloses that the InP-Sn solution was in a graphite cup having a plurality of holes and loaded in a conventional liquid phase epitaxial boat directly over the InP substrate being treated.
The article entitled, "Thermal Deformation of Surface Corrugations on InGaAsP Crystals" by H. Nagai, Y. Noguchi and T. Matsuoka, J. of Crystal Growth, Vol. 71, 1985, pp. 225-231, discloses a study of thermal deformations which arise during liquid phase epitaxial growth. The article is particularly directed to the loss of P atoms in distributed feedback laser diodes. The article states that providing an atmosphere of PH.sub.3 during the liquid phase epitaxial growth of a device having a layer of InP can be used to inhibit defects in this layer. The article reports that the PH.sub.3 was also effective in preventing defects in an InGaAsP surface during liquid phase epitaxial growth. The article recognizes that with the temperatures used in liquid phase epitaxial growth it is likely that a preferential vaporization of both As and P can occur. The primary solution to this problem reported in the article is the use of an atmosphere of PH.sub.3.
The article entitled, "Enhanced Indium Phosphide Substrate Protection for Liquid Phase Epitaxy Growth of Indium-Gallium-Arsenide-Phosphide Double Heterostructure Lasers", by P. Besomi, R. B. Wilson, W. R. Wagner, and R. J. Nelson, J. Appl. Phys., Vol. 54 (2) February 1983, pp. 535-539, discloses a method and apparatus using an InP-Sn solution within a conventional chamber during liquid phase epitaxial growth to inhibit thermal damage in an InP substrate. The article does not address thermal damage due to the loss of As atoms because only the InP layer was studied.
As used herein, the terms "chemically bound phosphorus" and "chemically bound arsenic" refer to compositions in which phosphorus and arsenic atoms, respectively, are chemically bound such as InP, InGaAsP and the like. Typically, an InP layer and an InGaAsP layer are present in laser diodes.
The loss of As and P atoms during liquid phase epitaxial growth is more likely to occur if a layer containing one of these atoms is exposed. This is the case for a solid state device such as a laser device which is formed by a fabrication process including the steps of etching layers and thereafter carrying out a liquid phase epitaxial regrowth. An exposed active layer (InGaAsP) can lose both As and P atoms.